Document DD 158 019 A1 discloses a listening/speaking set for casual divers. In this case, the set consists of an earpiece and a body contact microphone, which are integrated in an elastic, waterproof and functionally designed molded part such that the earpiece is located directly in front of the ear and the contact microphone is located on the neck next to the larynx. A disadvantage of such a set is that the earpiece must be positioned directly in front of the ear in a waterproofed manner.
Furthermore, from JPH 0368226 A, underwater communications equipment which operates by ultrasound is known.